We all think we can imagine a perfect beach. But what is it that makes one strip of palm-shaded ocean-scoured sand better than any other?

Many of the beaches of the Seychelles come pre-packaged with unique selling points: this, you discover, is the Bounty Bar Beach and that, a lone palm tree stretching out nearly horizontal to the ocean, is the Bacardi Beach. On your right, a guide informs you matter-of-factly, pointing toward a slim crevice in the cliff, is 'Robinson Crusoe's cave', while 'in front of you The Blue Lagoon was filmed with Miss Brooke Shields'; a little further on, you arrive at 'the location for Emmanuelle with Miss Sylvia Kristel'.

But there are a couple of stretches of sand on the islands which purport to go one better even than these eclectic celluloid fantasies. Up in the north-west corner of Praslin, the second largest of the Seychelles main group of islands, are what, by some accounts, are the two finest beaches in the world. Who says so? Well, some German tourists, of course, who got here first and who had a notion that things like perfection are best quantified.

Still, when a Berlin-based travel magazine invited its readers to nominate their favourite places on Earth to pitch towels, in first place they ranked Anse Lazio on the northern tip of Praslin and in second place they nominated Anse Georgette a mile to the south. Spend a day on either and, while acknowledging that both would be hard to beat, you come to realise that a beach hit parade is a subjective business.

Despite their proximity, the two beaches could hardly be more different: Anse Lazio boasted a car park full of four-wheel drives and a large restaurant and was relatively dense with afternoon bathers; Anse Georgette was accessible only by boat, or by strong swimmers, or overland through a stretch of jungle in the torpid heat, and was deserted.

In a vague attempt to bring some science to the question, I sat in the circle of shade cast by the ancient and low slung takamaka tree that provides a landmark at the back of Anse Lazio, and lay subsequently in the afternoon sun on Anse Georgette, and squinted half-heartedly at a recently published doorstop tome on the idea of The Beach , written by American academics Lena Lencek and Gideon Bosker (and not to be confused with Alex Garland's somewhat better selling book of the same name), which promised to offer a detailed biography of paradise.

In the rather exhaustive view of Lencek and Bosker - and their treatise took into detailed account 'the discreet charms of the bourgeois beach' and the particular pleasures of the 'blue-chip beach', the 'erotic beach' and the 'edifying beach' - the ideal Anse, it seems, 'collapses past and present into a matrix of water, sand, space and light, and moves us with the power of a drug, reorienting our sense of time and firing our slumbering hedonism'. After some (reoriented) hours of research, and the odd invigorating entanglement in the matrix of water and light (dips in the sea) I decided that both beaches succeeded on all counts (though if pressed I'd probably have my ashes scattered on Georgette).

For all their beauty, though - and their firing of slumbering hedonism - beaches are not wholly the point of a holiday in the Seychelles. In many ways they should be seen simply as spectacular arrivals and departures lounges as you tour the islands by boat.

The Seychelles are made for tropical Swallows and Amazoning, and Praslin, centrally located and accessible by air from the main island, Mahe, makes the perfect base: a little less busier than Mahe (Prasliners refer to Victoria, the world's tiniest capital, with shakes of their head, as if it was south-central Los Angeles) it none the less boasts some great places to stay, none better than the newly opened and spectacular Lemuria Resort, with its new championship golf course hanging over the sea and where, for example, if you play tennis, you may well be offered champagne, between points.

In just under a week we visited half a dozen different islands from Praslin: some, like Coco Island, only smooth grey protrusions from the sea that provided anchorage for snorkelling - which including the thrill of swimming above a sea turtle as it made its thoughtful way between rocks, eyes blinking studiously; others big enough to have cemented their own particular culture: cars are banned, for example, from La Digue (a favourite destination of the Blairs), and we toured the island south to north raindrops-keep-falling-on-my-head style on boneshaking bikes (ox carts are the alternative, more sedate option).

As well as its own atmosphere, each of the islands boasts its own flora and fauna. On Praslin, most spectacularly, the extraordinary coco-de-mer plants grow in the island's protected central rainforest, the Vallée de Mai: vast trees that produce phallic catkins and wonderful buttock-shaped nuts, and which 'mate' (there are males and females) only on stormy nights, or by the light of the full moon, or when they are in the mood, depending on which myth you want to believe. (General Gordon of Khartoum was so entranced by this place that he declared it the original site of the Garden of Eden and the coco-de-mer the tree of life; his belief is given slightly more weight by the fact that, oddly, and despite many efforts over the centuries, the trees will propagate nowhere else on earth). On Curieuse, a half-hour boat trip to the north, we walked among the famed giant tortoises - 250 live and breed here and roam freely - which tore slowly at grass and occasionally rose on their haunches and mooched past each other, apparently frustrated with the paparazzi; while on Aride, further north again, half a million seabirds wheeled around the sheer granite cliffs, overseen by frigate birds, with their enormous wingspans, hovering.

Apart from its its teeming bird population Aride is home to a nesting pair of British ornithologists, happily named Janet and John, who have lived here as virtual Crusoes for a couple of years with a small team of local volunteers. The group live in a makeshift compound of huts near the water's edge, by day studying the birds and turning out en masse to help the odd tourist boat through the heavy surf; by night attempting to protect the birds' nesting sites from poachers, who have, in the past, been known to make off with as many as a 1,000 eggs in one landing. The poachers can be fairly ruthless, Janet explained, and the islanders are armed only with 'torches and polite persuasion', but still this year the numbers of thefts has decreased.

The group do a great little tour of the island, too: ours was conducted by Jimmy, a rasta twitcher, who led us animatedly through the forest collecting spices - ginger, saffron, aniseed - and carefully uncovering the ground-level nests of Noddy terns (there are no cats or rats on Aride to disturb them), pointing out flitting red-tailed tropic birds or letting Sooty terns perch on his shoulders, a dreadlocked Dr Dolittle. Jimmy, a native of Praslin, has lived here for a couple of years, and rarely ventured back to the bigger islands. He explained, smiling broadly, that the only thing he really missed were 'women, I guess'; Janet and John meanwhile, who joined us for a beach picnic, their eyes lighting up at the sight of strawberries, confessed to craving chocolate the most - somewhat ironically since the island is owned and protected by the Cadbury family. James Cadbury is an annual visitor, but even his rations, it seems, are quickly consumed.

Over lunch John explained how they came to be here: they were selected Castaway -style from dozens of other applicants, on their perceived ability to survive together alone; John had spent the previous nine years studying swans bottoms for a Phd: his theory - which proved that the larger the bottom the more successful the female - was one of the few works of doctoral biology to have aroused the interest of the Sun .

John's theory seemed to hold true, too, in Praslin's main nightspot, Bufe (the cupboard), into which entire younger portion of the island's 6,000 inhabitants squeezed every Friday and Saturday night; hemp is dried on the beach nearby, so it was a mellow crowd that seemed suitably unfazed by the DJ's odd predilection for Shakin' Stevens. Bufe is just down the road from Praslin's newly built colonial-style casino: a good place to unburden yourself of troublesome Seychellois rupees, before watching seasoned locals clean-up on the blackjack tables.

The tourist brochures describe the Seychelles as 'unique by a thousand miles' and certainly moving between the islands you have a sense of being adrift from the rest of the world; there are no major diseases here, few mosquitoes, little apparent poverty - the islands enjoy the highest standard of living of any 'developing country' - and fairly relaxed mores: Praslin men, for example, frequently have children with four or five local concubinos.

Certainly, lying on Anse Georgette, past and present suitably compressed, you could half convince yourself that General Gordon was right all along; or perhaps it is just that 'matrix of water, sand, space and light' doing its particular stuff.

Getting there

Tim Adams stayed on Praslin at the five-star Lemuria Resort which can be booked through Classic Connection which offers tailormade itineraries to the Indian Ocean.

Lemuria Resort is the newest luxury five star property to open in the Seychelles. Prices for a seven night stay in a Junior Suite on a bed & breakfast basis start at £1694 per person, rising to £3086 per person in high season. Prices include return economy flights with Air Seychelles and private transfers.

Classic Connection also has a Caribbean, African and Worldwide portfolio.

Classic Connection: 01244 355 320